I'm not sure about MegaMacs, but PowerMax seems to get fairly positive reviews.

I would probably be more inclined to buy from eBay or Craigslist though. You shouldn't forget about refurbished Macs from Apple either. At least you're covered with a full one-year warranty that way. The deals they offer are pretty good too._________________2011 Mac mini with 8GB of RAM
2012 Mac mini Server with 16GB of RAM
46" Sony TV
24" HP LCD
Apple wireless keyboard and Magic Mouse
2 x 1TB MiniStacks
1TB MiniStack Max